I just listened to "The Widow's Assassin." Hoo boy...
A little backstory:
Back in 1986, the entire TV season consisted of the 6th Doctor going on trial for all of his meddling throughout time and space. It turns out that when the Time Lords teleported the Doctor into the court room, he was in the middle of an adventure with Peri, and Peri died in his absence. At the end of his trial, the Doctor was informed that Peri hadn't actually died, but was rescued by King Yrcanos (Brian Blessed's character), and was living the rest of her days on Yrcanos' planet as his warrior queen.
The Doctor never actually followed up on that. He never checked up on Peri to see if she was happy. He just left the court room, sent his future companion Mel back to his older self, and went on to have more adventures with Evelyn Smythe, Charley Pollard Mila, and Flip Jackson. Then Flip took an extremely suicidal risk, and the Doctor suddenly remembered how Peri almost died, and finally decided to go check up on her.
And that's where "The Widow's Assassin" comes in. The Doctor wants to pick up where he left off with Peri, but she's not having it.
The resulting story is surprisingly funny. I didn't expect this to be one of the sillier Who stories, but really is. There's a murder mystery, a policeman that's a talking sheep, two prison guards whose birth names are actually Guard One and Guard Two, and a princess attempting to find a suitor through speed-dating.
The only downside to this whole thing is that, when all is said and done, Peri ends up experiencing zero character growth.